It is known to swell tobacco and subsequently subject it to heat-treatment in order to improve the filling capacity thereof.
Swelling processes with volatile organic compounds, e.g. according to U.S. Pat. No. 3,524,451 have the disadvantage that most organic solvents are unsuitable for use on an industrial scale due to their flammability. Halohydrocarbons also are unsuitable because they are prejudicial to the environment.
The swelling of tobacco with nitrous oxide according to U.S. Pat. No. 1,374,420 or with SO.sub.2 according to U.S. Pat. No. 1,375,820 is also disadvantageous because, under certain conditions nitrous oxide can support combustion and is physiologically objectionable, while sulphur dioxide has strong reducing, bleaching and irritating properties.
The process of U.S. Pat. No. 3,778,533 proposes impregnating the tobacco with ammonia and carbon dioxide to make tobacco expand, but the ammonium carbonate which forms in situ can, under certain circumstances be left behind in the tobacco.
Finally, it is known, e.g. from U.S. Pat. No. 2,344,106 to use steam, air or CO.sub.2 as swelling agents. However, steam and air have only a moderate swelling action, while there are objections to carbon dioxide in the case of basic tobaccos because an interaction is possible with the amine components of the tobacco.
In a process for improving the filling capacity, it is important not only to produce a volume increase, but also to retain the elasticity of the fibrous structure. Thus, although certain swelling agents bring about a considerable increase in the volume, the filling capacity is not improved if the cellular structure of the fibres is involved to such an extent that on further processing the tobacco crumbles or disintegrates to powder.
The problem of the invention is therefore to provide a process for improving the filling capacity of tobacco in which the taste acceptance of the tobacco is not impaired and in which the process can be performed in such a way that it is less costly from the apparatus and energy standpoints, can be performed in a much shorter time and is not prejudicial to the environment.